textproduct: Rapid City

KEY MESSAGES

- Upper ridge will dominate the weather through next week.

- Thunderstorm areal coverage will increase tonight and hang about into next week, although in the hit or miss variety.

- Isolated strong/severe thunderstorms may occur during the later afternoon/evening hours through Tuesday.

- Temperatures will average 4-8F above normal.

UPDATE

Issued at 1051 PM MDT Sat Aug 22 2026

Updated PoPs and QPF overnight to better capture latest model guidance and current radar trends. Models continue to show significant disagreement on placement of potential thunderstorms Sunday afternoon and evening, and have been changing from run to run as well. Have taken a broad-brush approach with low PoPs for now, favoring the Black Hills and most of our South Dakota plains (especially north of I-90 and then east of the Badlands). We'll continue to try to refine this over the next 36 hours. Parameters continue to support the potential for a couple severe thunderstorms with damaging wind and large hail risks.

DISCUSSION

(This Evening Through Saturday) Issued at 1236 PM MDT Sat Aug 22 2026

18z surface analysis had weak high over the northern Plains into the middle MO river valley. Weak frontal boundary behind it from central MT into eastern CO. Patch of low stratus over western NE has been pushed northwestward on southeasterly winds along boundary leading to upper 50s Td/s across parts of northeastern WY. Water vapour matinee depicted shortwave ridge over the CWA, but shortwave trough hot on it's heels over eastern ID/western WY. Lift ahead of wave leading to some weak radar returns over northeastern WY, but nothing below 12kft per KGCC observation. Main concern this forecast is convection.

Later this afternoon/evening, around 1500J/kg MLCAPE pools along frontal boundary with weak MLCIN. Shortwave overtops, which will assist convective initiation. Perhaps 20-30kt effective shear will be present, enough to support isolated strong/severe thunderstorms where SPC Day 1 Marginal in place. Storms will slowly move eastward across the CWA tonight, but in weaker fashion over western SD given less favorable environment. Temperatures will be near guidance.

Sunday, aforementioned frontal boundary ends up over the western SD plains, influenced by tonight's convection/outflow. The further east it goes, the less the effect on the CWA. Right now, HREF suggests it'll settle over the eastern quarter of the CWA. 2KJ/kg CAPE pools along it with 30-40kts of 0-6km shear sufficient for strong/severe thunderstorms. Some CAM guidance suggests a supercell or two dropping south along the UNR/ABR border area late in the day. Temperatures will be near guidance.

For Monday/Tuesday, disturbances rotating around the upper ridge will support additional chances for strong/severe convection given forecast shear/buoyancy profiles. The rest of next week looks less active as upper ridge/height rises more dominant.

AVIATION

(For the 06Z TAFS Through 06Z Sunday Night) Issued At 1038 PM MDT Sat Aug 22 2026

Showers are moving eastward out of WY and over the Black Hills onto the SD plains. These should move out by sunrise. A front will pass through northeastern WY early Sunday afternoon, shifting to north winds. Assuming appreciable surface heating, TS conditions are possible across most of the area, primarily over the Black Hills and east. Confidence in timing/placement is still low. Regardless, have introduced a PROB30 for KRAP for Sunday evening.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.